In general, a door is installed in a building such that a user can come in and out through the door. The door is provided with an apparatus for opening and closing a door such that the door can rotate around a plurality of hinges mounted on the face of both the door and a doorframe.
There are various types of apparatuses for opening and closing a door. In recent days, there has been developed an apparatus for opening and closing a door in which a hydraulic hinge and a spring-type hinge form a couple of hinges for the purpose of promoting a user's safety and convenience in use. In the apparatus for opening and closing the door, the hydraulic hinge and the spring-type hinge are mounted between the upper end and the lower end of the door and the doorframe, respectively, so that an opened door can be automatically and slowly closed.
The hydraulic hinge and the spring-type hinge included in the apparatus for opening and closing the door are complex in structure and so difficult to manufacture and repair that it is almost impossible to repair them upon the occurrence of failure in the hinges.
Further, the hydraulic hinge is structured such that oil contained in a cylinder is circulated through a passage having a too small diameter when the door is opened and closed. As a result, the passage tends to be clogged up with foreign matters contained the oil and accordingly the function of the hydraulic hinge deteriorates. Thus, a user suffers from a trouble of frequently replacing the hydraulic hinge should by new one, thereby increasing economic burden.
Furthermore, in the hydraulic hinge of the conventional apparatus for opening and closing the door, a piston is coupled to a piston guide in such a manner that guide pieces formed on both sides of the piston are fitted into guide grooves formed on the piston guide. In consequence, a twisting force is generated in the guide pieces when the door is opened and closed, thereby causing the guide pieces to be incurably deformed and damaged.
Meantime, in the spring-type hinge of the conventional apparatus for opening and closing the door, both ends of a spring are directly fixed to a rotary member and a fixed member, respectively, such that there is generated only compressive tension in proportion to the radius of rotation of the door. Consequently, a force for opening and closing the door is inevitably weak, and an elastic force of the spring deteriorates when the spring-type hinge is used for a long period of time.